The present invention relates to a measuring device and, more particularly, a measuring device which continuously measures the temperature corresponding to the dew point of flue gases. This device is related to the apparatus described in previously issued U.S. Pat. No. 3,930,398, dated Jan. 6, 1976. In that apparatus, a signal representative of the dew point controls certain heating and cooling apparatus dependent on the formation of a thin condensate film from the flue gases. In that apparatus, the signal is applied through various electronic equipment to control a heating element and a coolant flow valving system. Between the heating element and the cooling apparatus, the rate at which condensation forms on the surface is controlled. It further insures control of the temperature of the surface which is exposed to the flue gases. It can manipulate this surface temperature upwardly or downwardly as required.
All values of temperature of the condensing surface exposed to the flue gases are received by the temperature recorder for continuous monitoring and manipulation of these values. This continuous signal enables continuous measurement of the dew point temperature with a useful level of accuracy and with minimum fluctuations when the dew point temperature approaches near the temperature of the condensation surface. There are, however, limitations on the operation of the disclosed apparatus.
One limitation on the apparatus of the above discussed patent occurs if the dew point temperature is lower than the temperature of the condensation surface. At this point in time, the surface is too hot to permit condensation, and, accordingly, the apparatus does not form a signal indicative of dew point temperature. It is known that it is somewhat lower, but it is impossible to know how much lower the actual dew point temperature is.
Conversely, when the temperature of the flue gases flowing past the condensation surface is considerably higher than the dew point temperature, then the dew point temperature of the flue gases is difficult to measure because of the great gap. In other words, the large differential temperature makes it difficult to obtain a correct measure of the dew point temperature, and, with this difficulty, there is difficulty in correctly controlling application of the heating and cooling means.
The apparatus of the above mentioned patent is capable of tracking the dew point temperature of the flue gases within certain accuracy limits. These accuracy limits are unduly broad or wide, and, accordingly, the present invention is able to track the dew point temperature variations and fluctuations with much greater accuracy.
The present invention is, by contrast, a more accurate device for providing continuous control of dew point temperature measurements. Moreover, it is able to provide dew point temperature measurements over a wider range of fluctuations, thereby permitting it to be used in different situations. The dew point temperature of flue gases is, in part, dependent on many variables, including proximity to the furnace, the feed stock for the furnace, the presence or absence of sulfur in the coal in the furnace, heat exchangers in the stack, pollution control devices in the stack and so on. It will be understood that the above mentioned factors and other factors may cause the dew point temperature to fluctuate over an extremely wide range. In some instances, it may be quite low, while in other instances the normal operating dew point temperature will be comparatively high. Use of the present invention prolongs the life of large and expensive boilers and boiler related equipment. This is particularly true where the boiler is stoked with high sulfur fuels. High sulfur fuels present severe pollution control problems in that the sulfur cannot be permitted to escape to the atmosphere because it takes the form of various sulfur oxides. Sulfur oxides are considered detrimental to the environment and, therefore, require rigorous pollution control measures. The present invention cooperates with such controls and, more importantly, enables the life of large, expensive boiler installations to be materially extended.
This device utilizes an exposed condensation surface in the flue. The flue gases are conducted past the surface. By control or manipulation of the surface temperature, a thin film of condensate is formed on the surface. The present invention measures the point at which the condensate film is formed from the vaporized gases in the flue.